1. Field of the Invention
This invention relates to exposure apparatus and method used for fabricating semiconductor devices or the like, for example, to exposure apparatus and method that expose a pattern of a mask onto a substrate such as a wafer or the like, and particularly to exposure apparatus having an actuator to perform oscillation control.
2. Description of Related Art
Conventionally, in a lithography process, which is one of the methods of fabricating a semiconductor device, various exposure apparatus are used to transfer a circuit pattern formed on a mask or a reticle (hereafter referred to as a reticle) onto a substrate such as a wafer, a glass plate, or the like, coated with a resist (e.g., a photosensitive agent). For example, as an exposure apparatus for a semiconductor device, in response to making a minimum line width of a pattern more fine in order to improve the degree of integration of an integrated circuit, in recent years, a reduction projection exposure apparatus is mainly used to reduce and transfer a reticle pattern onto a wafer by using a projection optical system.
It is known to use a step-and-repeat type projection exposure apparatus or a step-and-scan type projection exposure apparatus as this reduction projection exposure apparatus. The step-and-repeat type reduction projection exposure apparatus (a so-called stepper) sequentially transfers a reticle pattern onto a plurality of shot regions (exposure regions) on a wafer while maintaining the reticle and wafer stationary. The step-and-scan type scanning exposure apparatus (a so-called scanning-stepper) transfers a reticle pattern onto respective shot regions on a wafer by synchronously moving a reticle and a wafer during pattern transfer. See, e.g., Japanese Laid-Open Patent Application No. 8-166043 (corresponding to U.S. patent application Ser. No. 08/539,080, filed Oct. 4, 1995).
In these exposure apparatus, in order to respond to the above-described fine pattern, positioning with high accuracy is necessary in addition to improvement of resolution. Because of this, alignment with high accuracy for a mask, a wafer, or the like, improvement of a servo system positioning capability for a mask stage, a wafer stage, or the like, improvement of vibration isolation from the surrounding environment, and the like is performed. For example, with respect to vibration transmitted through a floor or foundation, a base plate is first provided, which acts as a reference, on the floor. Most vibration can be controlled by using a main body column to support a reticle stage, a wafer stage, a projection optical system (projection lens), and the like, and then mounting the main body column to the base plate via damping units, which shield the components supported by the main body column from floor vibrations.
However, the following problems exist in the conventional exposure apparatus described above.
As the demand for positioning accuracy increases, it is important to control vibration caused by movements of components within the exposure apparatus. That is, the above-mentioned exposure apparatus sequentially repeats exposure for subsequent shot regions after the exposure for one shot region on the wafer is performed, such that a reaction force due to acceleration and deceleration of the wafer stage (in the case of a stepper) or the reticle stage and the wafer stage (in the case of a scanning-stepper) causes oscillation of the main body column and the attached projection optical system. This may cause the projection optical system to be displaced.
In this case, if a relative positioning error between a projection optical system and a wafer or the like is generated, a pattern is transferred to a position different from a desired position on the wafer. This causes positioning error and image blur (i.e., an undesired increase in the pattern line width). In particular, when there is a thin part or a hole in a portion of the projection optical system, as the oscillation frequency decreases and the oscillation amplitude becomes large, displacement of the projection optical system becomes large, and it is difficult to make a pattern fine.